So I recalibrated my probes and did a full battery of tests with a couple of surprises.
I found my temp. probe to be caked and my pH probe off by about .30. Salinity was also much lower than I normally keep it.
Salinity: 1.023 (refractometer)
Ca: 425 ppm (Seachem)
Alk: 9.0 ppm (Salifert)
NO2: Undetectable (Seachem)
NO3: Undetectable (Seachem)
pH: 7.93 (Probe)
Temp.: 77.5F (Probe)
Mg: 1410 (Salifert)
I do not have any tests for heavy metals, but it seems to that the likelihood of there being a heavy metal problem is extremely low, unless it is coming in my salt. I take great pains to mix salt with very pure water. Well, except for the gold ring I lost in the tank a year ago!
So the question is, are the low pH and salinity inclined to lower the clam health? I am slowly bumping both back up.